Ion Heating by the Current-Driven Electrostatic Ion-Cyclotron Instability

Abstract

We have observed and confirmed significant ion heating by the electrostatic ion-cyclotron instability in a barium plasma. We present spectroscopic evidence showing that this mechanism drastically alters the velocity distribution, demonstrating at least a highly nonlinear process and giving strong evidence for randomization of the particle motion. Experimental corroboration of a theory of Drummond and Rosenbluth is presentedWe report the direct observation of ion heating in a fully ionized barium plasma, as indicated by an order-of-magnitude increase in ion temperature (from 2500°Kto greater than 25 000°K) due to the current-driven electrostatic ion-cyclotron instability. 1 The instability was generated by a technique first used by Motley and D'Angelo in the Princeton University Plasma Physics Laboratory Q device, 2 the theory for which was subsequently developed by Drummond and Rosenbluth. 1 The experiment was performed in the Q machine at the University of California at Irvine. Perpendicular temperature measurements were made by spectroscopically observing the Doppler line broadening of light scattered by singly ionized barium after the techniques developed by Hinnov et al 3 The significance of these measurements is that this is the first demonstration of ion heating by this current-driven instability. 4 Historically, this series of measurements was undertaken in an attempt to explain the previous results of Hinnov et al. 3 They measured and reported anomalously high ion temperatures in a barium plasma but the heating mechanism was not understood. We repeated the earlier experiments and recovered some of their results. However, we noticed that high temperatures occured when the rhenium coating on the hot tungsten end plates, used to ionize the barium, 5 was uneven so that patches of tungsten appeared through the rhenium coating. As a consequence small areas of different work function were formed on the plates and we speculated that the localized emfs thus formed produced axial filaments of current (easily visible since the barium ions emit visible light). To test this hypothesis, and to identify the heating mechanism (which we were unable to do initially) we went to a single-ended Q machine with insulated buttons, as indicated schematically in Fig. 1(a). In this configuration the electrostatic ion-cyclotron instability was observed, easily identified from its spectrum, from its dependence on the magnetic field, and by recovering the results of Motley and D'Angelo, 2 most notably that the observed frequency is slightly higher than the ion-cyclotron frequency (typical values at onset: / ci = 5 kHz, / = 61 kHz, linewidth approximately 1 kHz). Several configurations were tried, varying from a single button to an BUTTON PROBE BARIUM OVEN TO FABRY-PEROT •5 FIG. 1. (a) Schematic of the experimental arrangement. The length L was 123 cm; the diameter, 5 cm, button diameter, 0.6 cm. The Fabry-Perot looked into a light dump also, (b) Typical low-temperature (T f ) Doppler broadening scan. a 0 is the 4934 A line of Ba n, ...

Laboratory simulation of broadband ELF waves in the auroral ionosphere

“…Electrostatic ion-cyclotron waves are particularly well suited for perpendicular ion heating because of the resonant coupling between the fluctuating wave electric field and the ion gyromotion [Rynn et al, 1974;Dakin et al, 1976]. The notion that electrostatic ion-cyclotron waves should be present in space originates from early laboratory experiments demonstrating the relatively low excitation threshold of such waves [DMngelo and Motley, 1962], the subsequent theoretical work that provided a framework with which to understand the instability mechanism [Drummond and Rosenbluth, 1962], and the availability of free energy from parallel currents in the highly structured and nonequilibrium high-latitude ionosphere.…”

CLASSIFICATION OF FOUR-DIMENSIONAL INTEGRABLE HAMILTONIAN SYSTEMS AND POISSON ACTIONS OF $ \mathbb{R}^2$ IN EXTENDED NEIGHBORHOODS OF SIMPLE SINGULAR POINTS. II

“…The density ratio of the hot-tail ions to the bulk ions, T I & , , increases with an increase in V,. For R, = 1.0, however, it does not exceed a few percent (RYNN et al, 1974;CORRELL et al, 1977, in which the ion heating due to the instability was also reported, although the two-component structure of the energy distribution was not observed). When we increase R, up to 1.3, a clear increase of It, is observed and, for V, 5 50 V, the distribution is almost one-component Maxwellian, having the high temperature.…”

“…Under a uniform magnetic field, the instability excited shows a frequency spectrum having a peak a little above the ion-cyclotron frequency wci/27r. This instability has been regarded as a current-driven electrostatic ion-cyclotron instability (MOTLEY and DANGELO, 1963;RYNN et al, 1974;CORRELL et al, 1975CORRELL et al, , 1977, although other mechanism for the excitation was proposed, taking into account the sheath in front of the driving target (LEVIN and KUCKES, 1966). When R, is changed for a fixed value of B at the mirror center or at the mirror points, the frequency is observed to depend only on B at the mirror point where the small driving target is set.…”

Formation of wave-front pattern accompanied by current-driven electrostatic ion-cyclotron instabilities

“…5,6 The experimental results are said to be explained by the theory developed by Drummond and Rosenbluth. 1 In the usual Q-machine experiments, a positive potential is applied to a small electrode in the plasma to induce an electric current, so the electric field has not only a component along the magnetic field lines, but also a component across the magnetic field lines.…”